Convergence Components RandD Division

KETI, South Korea

Convergence Components RandD Division

KETI, South Korea
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Kang D.H.,University of Suwon | Lee B.S.,University of Suwon | An H.K.,University of Suwon | Kim Y.H.,University of Suwon | And 3 more authors.
Materials Letters | Year: 2010

Sodium bismuth titanate (NBT) thin films substituted with yttrium for Na site were prepared by a modified sol-gel processing and their dielectric properties were investigated. The stability of perovskite structure was highly affected by the amount of Y substitution and the annealing temperatures. Y substituted NBT thin films post-annealed at 750 °C exhibited uniform microstructures associated with grain growth inhibition. Relative permittivity and remnant polarization were maximized at 5 mol% Y substitution and loss tangents for all the prepared films were relatively stable with less than 0.03. It was also found that the substitution of yttrium led to the enhancement of diffuse phase transition for the NBT thin films. © 2010 Elsevier B.V.


Ullah A.,University of Ulsan | Ahn C.W.,Convergence Components RandD Division | Kim I.W.,University of Ulsan
Physica Status Solidi (A) Applications and Materials Science | Year: 2010

Lead-free (1 - x)(Bi 0.5(Na 0.85K 0.15) 0.5TiO 3)-xBiAlO 3 (abbreviated as BNKT15-BA, x=0, 0.025, 0.050, 0.075, 0.100) piezoelectric ceramics were synthesized by a conventional solid-state reaction method. The phase-transition behavior in BNKT15-BA ceramics with respect to changes in composition were investigated using X-ray diffraction analysis, dielectric and ferroelectric characterizations, and electric-field-induced strain. The results of X-ray diffraction revealed that a pure perovskite phase was formed for x ≤ 0.050. A phase transition from the coexistence of rhombohedral and tetragonal to a pseudocubic phase was observed at x=0.050. The dielectric constant continuously decreased with increasing BA content, and the depolarization temperature (T d) was shifted towards lower temperature. The polarization and strain hysteresis loops indicate that the ferroelectric order of BNKT15 ceramics is disrupted significantly with the addition of BA. The destabilization of ferroelectric order is accompanied by an enhancement of bipolar and unipolar strains, and a large electric-field-induced strain (S=0.21%) and a normalized strain (d 33 *=S max/E max=276 pm/V) were obtained at x=0.050. These results suggested that the BNKT15-BA system can be employed in lead-free electromechanical devices. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Lee S.Y.,University of Ulsan | Ahn C.W.,University of Ulsan | Kim J.S.,University of Ulsan | Ullah A.,University of Ulsan | And 5 more authors.
Journal of Alloys and Compounds | Year: 2011

Piezoelectric (K0.5Na0.5)NbO3 (KNN) and (K0.5Na0.5)(Nb0.7Ta0.3)O 3 (KNNT) thin films were prepared via chemical solution deposition. An analysis of X-ray diffraction revealed that Ta5+ diffuses into the KNN to form a single perovskite structure. Compared to KNN films, KNNT films exhibited a low leakage current density due to their fine-grain nonporous structures. The partial substitution of Ta5+ for the B-site ion Nb5+ in the KNNT films decreased the Curie temperature (T C). This in turn led to the existence of a polymorphic phase transition near room temperature and further improvement in the piezoelectric properties. Lead-free KNNT films exhibited a well-saturated piezoelectric hysteresis loop with a effective piezoelectric coefficient (d33,eff) value of 61 pm/V, comparable to that of PZT thin films. © 2011 Elsevier B.V. All rights reserved.


Kim III W.,University of Ulsan | Ullah A.,University of Ulsan | Ahn C.W.,Convergence Components RandD Division | Hussain A.,University of Ulsan | And 2 more authors.
Journal of Alloys and Compounds | Year: 2011

In this study, lead-free 0.975[Bi0.5(Na1-xK x)0.5TiO3]-0.025BiAlO3 piezoelectric ceramics (BNKT-BA) with x ranging from 0 to 0.25 were fabricated using a conventional solid state reaction. The effects of potassium concentration (x) on the structure and electrical properties of the ceramics were investigated. The X-ray diffraction patterns revealed that the addition of K+ improved the crystal symmetry of the BNKT-BA ceramics and produced a rhombohedral- tetragonal morphotropic phase boundary (MPB) in the range of 0.15 ≤ x ≤ 0.20. The increase of the K+ concentration resulted in a decreased grain growth rate and promoted the formation of grains with a cubic shape. The BNKT-BA ceramics exhibited high remanent polarizations of 25 μC/cm 2 near the rhombohedral side of the MPB composition (x = 0.15). The polarization and strain hysteresis loops demonstrated that an increased K + concentration (x ≥ 0.20) destabilized the ferroelectric order of the BNKT-BA ceramics, leading to degradation of the remanent polarization and coercive field. However, the destabilization of the ferroelectric order was accompanied by significant enhancements in the bipolar and unipolar strains. A large electric field-induced strain (S = 0.33%) and a corresponding normalized strain (d33=Smax/Emax=533pm/V) were obtained on the tetragonal side of the MPB composition (x = 0.22). © 2010 Elsevier B.V. All rights reserved.


Lee S.Y.,University of Ulsan | Kim J.S.,University of Ulsan | Ahn C.W.,Convergence Components RandD Division | Ullah A.,University of Ulsan | And 2 more authors.
Current Applied Physics | Year: 2011

Lead-free (K0.5Na0.5)(Nb0.7Ta 0.3)O3 (KNNT) piezoelectric thin films were prepared on Pt(111)/TiO2/SiO2/Si(100) substrates by chemical solution deposition method. The effects of annealing temperatures 550, 600, 650, 700, and 750 °C on microstructure, leakage current, ferroelectric, and piezoelectric properties of the KNNT thin films were investigated. The largest remanent polarization Pr (10.5 μC/cm2), piezoelectric coefficient d33 (62 pm/V), and lowest leakage current density (4.6 × 10-6 A/cm2 under 120 kV/cm) of the KNNT film were obtained with annealing at 700 °C. The mechanisms concerning the enhancement in d33 are discussed, and the improved piezoelectric performance of the KNNT film suggests a promising candidate for piezoelectric thin film devices. © 2011 Elsevier B.V. All rights reserved.


Ullah A.,University of Ulsan | Ahn C.W.,Convergence Components RandD Division | Hussain A.,University of Ulsan | Kim I.W.,University of Ulsan
Current Applied Physics | Year: 2010

Lead-free Bi0.5(Na0.78K0.22) 0.5TiO3 (BNKT) piezoelectric ceramics were synthesized by the sol-gel technique. The effects of sintering temperatures on the crystal structure, microstructure, densification, dielectric, ferroelectric and electric field-induced strain behaviors of the BNKT ceramics were investigated. X-ray diffraction patterns exhibited a pure perovskite structure from 1075 to 1150 °C. A scanning electron microscopy study revealed an increase in grain size with increasing sintering temperature. The density of the ceramics sintered at 1150 °C reaches a maximum value of 5.55 g/cm3, which is 96% of the theoretical density. BNKT ceramics sintered at an optimum temperature of 1150 °C exhibited a high remnant polarization of 18.5 μC/cm2, a high electric field-induced strain of 0.20% and dynamic piezoelectric coefficient d33 = (Smax/Emax) of 247 pm/V. © 2010 Elsevier B.V. All rights reserved.

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